PNNL

Abstract

Structural Fe(II) in reduced iron-containing clay minerals (RIC) was documented to be bactericidal at pH 6, but suffers from weak efficacy at pH 7 and 8. Here we demonstrated an enhanced antibacterial activity of chitosan-intercalated reduced nontronite (rC-NAu-2) relative to unmodified reduced nontronite (rNAu-2). The antibacterial activity of rC-NAu-2 was more effective, efficient and persistent against a broader spectrum of human bacterial pathogens over a wider pH range, even at a lower clay concentration relative to rNAu-2. Relative to rNAu-2, rC-NAu-2 generated a lower amount of extracellular •OH production and Fe concentration, but a higher level of intracellular ROS accumulation and Fe content. In-situ imaging revealed that the membrane damage, reactive oxygen species and labile Fe enrichment of rC-NAu-2 treated E.coli cells were no longer restricted to polar regions, where cardiolipin occurred, as rNAu-2 treated E.coli cells did. The bactericidal activity of RIC was mainly attributed to the amount of effective•OH generated from clay surface, whose effect was largely dependent on the physical contact between RIC and E.coli cells. The tight attachments of positively charged rC-NAu-2 particles to cell surface promote •OH effectiveness and result in a higher bactericidal capability. These results advance the previously published antibacterial model by highlighting the important role of cell-clay spatial associations in the antibacterial activity of Fe-bearing clay minerals.